The present invention relates to improved cooking vessels, particularly to double wall cooking vessels, and in particular to methods of forming double wall cooking vessels used in induction cooking.
Double wall cooking vessels have a solid bottom surface and a pair of concentric co-axial sidewalls separated by an air gap there between. The double wall construction provides insulation so that the food stays warm after cooking, permitting the same cookware to be used as serving ware at the table.
Also known in the art is “waterless cookware”, which is a cooking vessel with a self-sealing lid so that a minimum of water is used to cook the food, with the steam generated from the added water and the foodstuff itself is retained, rather than lost through the gap between the vessel's rim and cover. The extreme example of “waterless cookware” is a pressure cooker, in which a pressure containing cooking vessel has a matching lid that locks to secure a gasket between the rim and the lid. The lid must have a pressure release valve, lest the internal pressure cause a violent explosion of the vessel. The other form of “waterless cookware” involves a pot or vessel rim that extends outward from the vessel's perimeter to provide a slightly concave region where steam can condense between the extended rim and the matching lid, thus forming a “water” seal in placed of the rubber gasket in the pressure cooker. The mass of the lid serves as a “release valve” preventing excess pressure within the confined volume that holds the foodstuff. Both forms of “waterless cooking” are popular as they offer a superior method of preserving vitamins, nutrients and natural flavors, creating a more pleasing and uniform texture to the cooking food than microware methods.
Double wall cookware however has certain disadvantages. The contained wall must be sealed from water for the expected lifetime of the product, as any water that enters or seeps in during use or washing presents a hazard when converted to steam during cooking. Thus, the cookware is difficult to manufacture, as well as costly.
Dual wall cookware also suffers in performance relative to single wall cooking vessels, as the outer surface near the bottom of the vessels is easily overheated during cooking, being insulated from the remainder of the vessel.
This rapidly leads to discoloration, and distortion under extreme conditions, making the cookware unattractive for use at the table, or display in the kitchen.
Induction heating is a preferred cooking method to save energy, but is also popular because the cookware heats rapidly. However, such cookware to be suitable for use with the widest variety of induction heating systems must include special magnetic alloys in the bottom. While such alloys can be incorporate in single wall cooking vessels by numerous methods, these methods provide additional complications that hinder the fabrication of dual wall cookware that has an air gap between the sidewalls.
Accordingly, there is a need for an improved dual wall cooking vessel and method of making the same that overcomes the aforementioned disadvantages, and in particular making the vessels suitable use with induction heating stoves or burners.
It is therefore a first object of the present invention to provide an improved construction for dual wall cookware.
It is a further object for providing a reliable and cost effective method of making such an improved construction, which results in a complete and secure seal at the rim where the inner and outer walls meet.
It is a further object of the invention that the securely sealing rim is suitably shaped so that the vessel may serve as waterless cookware with the appropriate matching lid.
It is a further object of the invention to provide a dual wall cooking vessel suitable for use in induction cooking, as well as for direct heating.